The present invention relates generally to an improved method and apparatus for protecting surfaces of a metallic object against corrosion while sealed within a plastic packaging envelope, and more particularly to such a method, apparatus, and package employing a vapor phase corrosion inhibitor (VCI) in the adhesive and film utilized in forming the packaging including the envelope so as to insure dispersal of the inhibitor throughout the package during its formation and thereafter. The method and apparatus of the present invention has been found effective in protecting the surfaces of metallic objects enclosed within plastic packaging envelopes, while at the same time, posing no threat to either the environment or the ultimate user of the object being protected. The present invention employs a vapor phase corrosion inhibitor in the packaging film and a substrate coated with a thermally activated adhesive (containing a vapor corrosion inhibitor) so as to complete the formation of the protective enclosure while simultaneously dispersing the corrosion inhibitor within the interior of the envelope. In this manner, a consistent and uniform film of inhibitor is made available for the long term protection of the metallic object.
Plastic packaging processes are widely used in the packaging of articles, particularly for display in vending. In particular, plastic packaging is widely utilized in packaging for display at retail, either on racks, in bins, or the like. Typically, skin packaging operations employ a substrate board of low density and high porosity and having an adhesive coating thereon, upon which the product is placed. Thereafter, a film is bonded to form the package, with the board and film enveloping and capturing the product therewithin. In these operations and in forming the package, the film is typically heated to a formable temperature, and thereafter placed in contact with the adhesive film on the surface of the substrate, and with a vacuum being utilized to draw the film tightly around the product secured therewithin.
Blister packs including blister shells formed from polyvinylchloride (PVC) or other suitable film forming resins are also widely used with the preformed blister being bonded to a heat activated resin coated on a board substrate to form the completed enclosure.
While conventional skin and blister packaging applications provide protection for the article for mechanical purposes prior to sale to the ultimate consumer, these types of packaging may require additional protection to inhibit potential damage from humid and/or corrosive environments. For example, the high porosity substrate required for the vacuum draw operation permits the subsequent introduction into the package envelope of water vapor and other potentially harmful gaseous components. Included in these gaseous components are various sulfides such as hydrogen sulfide and certain air-borne mercaptans, all in addition to the universally present water vapor. These corrosive components may be introduced into the envelope during extended shipping and storage times typically encountered between the completion of the packaging operation and the final transfer of the product to the ultimate consumer. These periods normally include time involved in final display for retail purposes. Blister packaging operations expose the packaged articles to the same corrosive components as skin packaging applications, with the additional possible exposure to gases created in any breakdown of the PVC components of the envelope.
Newly manufactured metallic articles frequently have fresh metal surfaces which are highly susceptible to corrosion, and as indicated above, corrosion may occur as a result of exposure to corrosive gases typically found in the ambience as well as those which may develop from the PVC envelope. Humid environments are almost universally encountered with varying degrees of severity. Fluctuations in temperature can cause condensation of the trapped water vapor and ultimate deposition of the condensate on metallic surfaces. Additionally, the presence of even minute quantities of corrosive gases such as hydrogen sulfide and various mercaptans may cause surface corrosion and ultimate cosmetic deterioration and in certain instances, mechanical deterioration of the article. The polyvinylchloride film utilized in most blister packaging operations is a possible source of chloride which is especially corrosive to many metallic articles. In certain aggravated circumstances, serious mechanical as well as cosmetic deterioration may occur so as to render the product as well as the package worthless. As a result, therefore, a need has developed for providing added protection for metallic articles contained within packaging, particularly skin or blister packaging.
While various packages may be prepared with vapor phase corrosion inhibitors being applied to substrate boards alone, it has been found that the present invention provides significantly greater protection and conserves resources by careful and practical utilization of the inhibitor. Since plastic film packaging may be employed for a wide variety of applications, and since only a portion of these applications require corrosion inhibitors, the present invention provides a specific means for creating a continuous in-situ source for the compound forming the vapor phase corrosion inhibitor, and further provides a desirable mechanism for dispersing and retaining the inhibitor within the confines of the envelope as it is being formed and for a substantial period of time thereafter. As such, greater long-term protection is provided with uniform and practical dispersal of the corrosion inhibitor being achieved.